(1) Field of the Invention
The present invention relates to an electro-photographic development apparatus employed in electro-photographic image forming apparatuses such as copiers, printers, and facsimiles, particularly to electro-photographic development apparatus using a single component developer.
(2) Description of the Prior Art
In a developing apparatus using a single component developer (toner), in general, the toner is supplied by a toner supply member such as a toner supply roller to a toner retaining member such as a developing roller. The toner layer thickness on the developing roller is adjusted by a toner layer thickness regulating member and the toner is electrically charged by the regulating member. The toner thin layer on the developing roller comes close to or into contact with an image retaining member such as a photoreceptor drum, thereby developing an electrostatic latent image on the image retaining member.
When the toner layer thickness regulating member contacts the developing roller surface, larger-sized toners are separated away from the developing roller and smaller-sized toners are consumed first for the development, thereby gradually degrading the image quality.
Accordingly, the developing apparatus is divided into two chambers (a toner container and a toner supply unit), thereby additionally supplying the toner supply unit with the toners in the toner container in order to prevent the increase in the larger-sized toners.
Concretely, an opening is formed in a wall between the toner container and the toner supply unit. The increase in the larger-sized toner is avoided in such a manner that the opening is opened, only when the toners is introduced from the toner container to the toner supply unit.
However, the two chamber developing apparatus has a disadvantage that the toner supplied from the toner container does not circulate well and stagnates in the toner supply unit, because a lot of the toners is supplied along only one direction from the toner container to the toner supply unit, whereby the rotational load of the toner supply roller is increased and the toner cannot be stably supplied on the developing roller. Further, the toner is not sufficiently electrically charged, thereby possibly causing the image quality degradation such as an increase in a background fog.
Therefore, in order to solve the above-mentioned disadvantage, JP2003-255687A discloses that an opening member between the toner container and the toner supply unit is fixed over the upper end of the opening. Further, a projected portion projected toward the inside of the toner supply unit is provided at the lower free end of the opening, whereby the toner supply from the toner container to the toner supply unit is suppressed, when the toner supply becomes excessive. Concretely, the developing apparatus of JP2003-255687A as shown in FIG. 7 includes the toner container 2 and toner supply unit 1. There is provided between them an opening which has a backward flow prevention valve 9 for preventing the backward flow to the toner container 2 from the toner supply unit 1. Accordingly, the upper portion of the valve 9 is fixed over the upper portion of the opening, while the lower portion of the valve 9 is made free and a projection 10a is fixed with the valve at the toner supply unit side. According to the valve 9, the image degradation due to the toner size selection is prevented. The projection 10a prevents the over filling-up and the stagnation of the toner which induce insufficient charging by a toner layer regulating member 5 and the torque increase in the developing apparatus.
However, JP2003-255687A has a disadvantage that the projected portion 10a may possibly hits the toner supply roller and the opening is not sufficient opened, thereby obstructing the toner supply, if there is not provided a sufficient gap between the projected portion and the toner supply roller.
Particularly, the sufficient gap is hardly guaranteed by JP2003-255687A, when the developing apparatus is to be made small-sized.